Image segmentation using discrete cosine transfer data, and image data transmission apparatus and method using this image segmentation

ABSTRACT

An image-data transmitter, applicable to a FAX and an image file apparatus, receives image data including a plurality of image-data portions, and identifies the image data for each image-data portion so as to detect a kind of image data for each image-data portion, such as a binary image and a multilevel image. Then the image-data transmitter codes the image data for each image-data portion in accordance with a coding scheme corresponding to the kind of image data of the image-data portion. Thus, a coding efficiency and an image quality of a restored image are not so much degraded.

BACKGROUND OF THE INVENTION

The present invention relates generally to image-data transmitters, andmore particularly to an image-data transmitter which transmits a blendof binary and multilevel images to an external apparatus via a channel.The present invention is especially suitable for a facsimile apparatus(abbreviated FAX hereinafter), and an image filing apparatus.

A modified READ coding scheme (abbreviated MR hereinafter), a modifiedHuffman coding scheme (abbreviated MH hereinafter), and a modified MRcoding scheme (abbreviated MMR hereinafter) are often used to code abinary image, such as a character image; the MH is used for a group 3(abbreviated G3 hereinafter) FAX, and the MMR is used for a group 4(abbreviated G4 hereinafter) FAX. In addition, a new coding schemedesigned to perform a progressive build-up indication for a soft copycommunication, in which a whole binary image is roughly indicated firstand an image quality thereof becomes gradually improved, has beenproposed recently.

On the other hand, a discrete cosine transform (abbreviated DCThereinafter) coding scheme is often used to code a continuous multilevelimage, such as a color image. As an example of a DCT coding scheme, abase-line system using a color still picture DCT coding scheme iswell-known. As shown in FIG. 1, according to the system, a target imageis segmented into a plurality of blocks, each consisting of n*n(typically 8*8) picture elements (abbreviated pixels hereinafter). Eachblock is coded in accordance with a two-dimensional (abbreviated 2Dhereinafter) DCT coding scheme (in step P1). Then, the obtained n*n DCTcoefficients are divided by n*n thresholds stored in a quantizing tableTA (in step P2). Each of the DCT coefficients F_(uv) (u, v=0, 1, 2, . .. , n-1) represents a spatial frequency component for each block ofimage data; in particular, a coefficient F₀₀ represents a DC componentof the spatial frequency proportional to an average value of n,n pixels,and another coefficients represents an AC component thereof, thecoefficient becoming high as variables u and v become large. Next, adifference between a DC component of an arbitrary block and that of ablock prior to the arbitrary block is calculated (in step P3), and thenHuffman-coded with reference to a Huffman code table TB (in step P4). Onthe other hand, each AC component is zigzag-scanned as shown in FIG. 2so as to be converted into a one-dimensional (abbreviated 1Dhereinafter) series (in step P5). Then two-dimensional Huffman coding isperformed, with reference to the table TB, for data generated as aresult of coding a run length of zero data and a bit number of a validcoefficient (in step P6). After all the blocks are processed, a codingoperation is terminated.

However, image data including a blend of a multilevel image depending ontone and a binary image depending on resolution iscompression-oriented-coded in a single mode, a coding efficiency and animage quality of a restored image are much degraded.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea novel and useful image-data transmitter in which the abovedisadvantages are eliminated.

Another, more specific object of the present invention is to provide animage-data transmitter which performs different coding operations forrespectively different kinds of image data.

With the foregoing in mind, an image-data transmitter according to thepresent invention comprises image identifying means for receiving imagedata including a plurality of image-data portions, and for identifyingthe image data for each image-data portion so as to detect a kind ofimage data for each image-data portion, encoding means, coupled to theimage identifying means and compatible with plural kinds of codingschemes corresponding to a number of kinds of image data of theimage-data portions, for coding the image data for each image-dataportion in accordance with a corresponding one of the plural kinds ofcoding schemes, and channel-control means, coupled to a channel and theencoding means, for controlling transmission of the image data to anexternal apparatus via the channel.

In addition, the present invention provides a method for transmittingimage-data including a plurality of image-data portions to an externalapparatus via a channel, which method comprises the steps of identifyingthe image data for each image-data portion so as to detect a kind ofimage data for each image-data portion, coding the image data for eachimage-data portion in accordance with a coding scheme corresponding tothe kind of image data of the image data portion, and controllingtransmission of the image data to the external apparatus via thechannel.

According to the present invention, due to the image identifying meansand the encoding means, each kind of image-data is coded in accordancewith a desired coding scheme. Thus, a coding efficiency and an imagequality of a restored image are not degraded as much as those inconventional technology.

Other objects and further features of the present invention will becomeapparent from the detailed description when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a view for explaining an operation of a conventionalbase-line system;

FIG. 2 shows a view for explaining a zigzag scan performed by thebase-line system shown in FIG. 1;

FIG. 3 shows a block diagram of a FAX according to the presentinvention;

FIG. 4 shows a flow chart for explaining a transmission operationexecuted by the FAX shown in FIG. 3;

FIG. 5 shows a block diagram for explaining in detail an imageidentification procedure performed at one of steps of the flow chartshown in FIG. 4;

FIG. 6A shows a typical continuous multilevel image (a human picture);

FIG. 6B shows a pseudo gray scale image shown in FIG. 6A (a dot-mappicture);

FIG. 6C shows a multilevel image of a complicated design including manyhigh-frequency components;

FIG. 6D shows a character image;

FIG. 7 shows a view for explaining how the FAX shown in FIG. 3 judges acolor of a character image;

FIG. 8 shows a view for showing how the FAX shown in FIG. 3 judges ashape of the character image; and

FIG. 9 shows a flow chart for explaining a reception operation executedby the FAX shown in FIG. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 3 shows a FAX to which an image-data transmitter according to thepresent invention is applied. The FAX shown in FIG. 3 comprises a systemcontroller 2, a channel controller 4, a scanner 5, an image memory 6, acoder and decoder (abbreviated CODEC hereinafter) 7, a plotter 8, acathode ray tube (abbreviated CRT hereinafter) display 9, a controlpanel 10, and a secondary memory 11. The system controller 2, channelcontroller 4, scanner 5, image memory 6, CODEC 7, plotter 8, and CRTdisplay 9 are coupled to each other via a system bus 1. In addition, thesystem controller 2 is coupled to the control panel 10 and the secondarymemory 11. Moreover, the channel controller 4 is coupled to a telephoneline 3.

The system controller 2 controls operations of each element of the FAX.The channel controller 4, comprising an ISDN interface, which performs acircuit-switched connection between the FAX and an external apparatusvia the telephone line 3, and transmits/receivescompression-oriented-coded image data to/from the external apparatus.The scanner 5 generates image data by scanning a predetermined imagewith predetermined resolution. The image memory 6 stores various imagedata.

The CODEC 7 codes the image data generated by the scanner 5, and decodesimage data transmitted from the external apparatus via the channelcontroller 4. The CODEC 7 includes a plurality of CODEC parts each usinga different coding scheme; a color still picture CODEC part using a DCTcoding scheme for a continuous multilevel image, a Q CODEC part is usedfor a dot-map image, MH, MR, and MMR CODEC parts are used for acharacter image. These coding schemes are well-known, and thus adescription thereof will be omitted. The CODEC 7 further includestherein the quantizing table TA shown in FIG. 1, an inversion referencedetecting table TC, a level reference table TD, an image-attributememory, and a discriminative color table, which will be described later.However, these tables may be provided independent of the CODEC 7.

The plotter 8 plots out an input image or a processed image. The CRTdisplay 9 indicates the input image or the processed image on a displayunit. Thus, the CRT display 9 indicates image data stored in the imagememory 6. The control panel 10 includes operating elements forcontrolling this system and an indicator for indicating a systemcondition. An operator of the FAX inputs a predetermined command to theFAX via the control panel 10. The secondary memory 11 stores variousdata used for the system controller 2.

Next follows, with reference to FIG.4, a description of a transmissionoperation of the FAX.

When the system controller 2 detects a transmission command input by anoperator via the control panel 10 (in step S1), the controller 2 drivesthe scanner 5 (in step S2) and thus the scanner 5 generates image databy scanning a predetermined image on a document (in step S3). As aresult, the scanner 5 stores every 8-bit string of RGB signalcorresponding to the image data in the image memory 6 (in step S4), andthe image data stored in the image memory 6 is indicated on the CRTdisplay 9. Next, the system controller 2 transmits the image data storedin the image memory 6 to the CODEC 7. In response, the CODEC 7 segmentsthe image data into a plurality of blocks, and performs a 2D-DCT processfor each block of image data (in step S5). Subsequently, the CODEC 7identifies the image data so as to detect, for each block, its kind, andgenerate each corresponding kind of image plane (in step S6).Incidentally, rather than using the CODEC 7 to identify the image data,the FAX may further comprise image identifying means for identifying theimage data.

Next follows, with reference to FIGS. 5 and 6A to 6D, a detaileddescription of the image identification procedure in step S6. First, azigzag scan is performed for the image data which was DCT-processed instep S5, so as to convert DCT coefficients of AC components into 1Dseries (in step P10). This procedure is the same as the step P5 shown inFIGS. 1 and 2, and a description thereof will be omitted. As a result,the 1D DCT coefficients are expressed as a spectrum distribution, forexample, as shown in FIG. 6A to 6D. FIGS. 6A to 6D respectively indicatefour different kinds of image data. FIG. 6A shows a typical continuousmultilevel image, such as a human picture. FIG. 6B shows a pseudo grayscale image of the picture shown in FIG. 6A, such as a dot-map picture.FIG. 6C shows a multilevel image of a complicated design including manyhigh-frequency components. FIG. 6D shows a character image. In FIGS. 6Ato 6D, each vertical axis represents a DC component, and each horizontalaxis represents a frequency level. As shown in FIGS. 6A to 6D, the kindof each image data can be identified by checking a number of changes ofthe coefficients (an inversion frequency) at a low-frequency region anda level at a high-frequency region. Thus, the CODEC 7 checks theinversion frequency in the low-frequency region (in step P11) by usingthe inversion reference table TC storing thresholds of the inversionfrequency, each of which corresponds to each kind of image data, and thelevel at the high-frequency region (in step P12) by using the levelreference table TD storing thresholds of the level, each of whichcorresponds to each kind of image data. Then the CODEC 7 judges the kindof image data based on results in steps P11 and P12 (in step P13). Thejudgment result is stored in the image-attribute memory in the CODEC 7(in step P14). If the image data represents a multilevel image and is tobe coded in accordance with the DCT coding scheme, one of the quantizingtables TA in the aforementioned base-line system is selected so as todetermine a threshold matrix suitable for the multilevel image (in stepP15).

Referring back to FIG. 4, each kind of image plane is thencompression-oriented-coded (in step S7), and transmitted to the externalapparatus via the channel controller 4 and the telephone line 3 (in stepS8). When all the image data is completely transmitted (in step S9), thesystem controller 2 informs the control panel 10 of the termination, andassumes the waiting mode so as to terminate the transmission operation(in step S10).

If the image data represents a character image, a color of the characterimage is determined, with reference to color difference data, asfollows: If the color is close to achromatic, it is regarded as black.Otherwise, it is specified as a color close to that of the characterimage. The color of the character image is easily determined based onthe color difference signals Cb and Cr of the image data, as shown inFIG. 7. In FIG. 7, the discriminative color table correlates a pair ofcolor difference signals Cb and Cr with a color code representing thecolor of the character image. Thus, the CODEC 7 can judge the color ofthe character image from the discriminative color table. Then the CODEC7 stores the color code in the image-attribute memory therein.

On the other hand, a shape of the character image is determined from aluminance signal Y of the image data. As shown in FIG. 8, the image datais first binarized based on the luminance signal Y, and then thecharacter image is expressed via a bit map based on the binarizedresult. Subsequently, each character block density is detected so that ahigh density area thereof can be regarded as the character image andexpressed as one large block. Since one bit corresponds to 8*8 pixels ofthe original image, a memory having a small storage can be used. Whenthe large block is generated, the bit map is segmented into p*q mesheseach having, for example, 4*4 bits, so as to count every mesh of targetbits; i.e., if there are more than 8 bits in an arbitrary mesh, thearbitrary mesh is corrected so as to be treated as a bit representingthe character block, and filtered so as to correct its attributes.

Thus, a color attribute is checked for each large block of a characterarea. In case of concentrated color distribution, an average color blockis regarded as the color of the character image. However, if aremarkably different color group is included, the character image isregarded to be colored by two different colors and the character imageis divided into the different colors of the character image. During atransmission operation, a pair of a discriminative code and luminancecode may be transmitted to the external apparatus. Instead of dividingthe character image into the different colors of the character image, aluminance data and a color code may be transmitted to the externalapparatus.

Next follows, with reference to FIG. 9, a description of a receptionoperation of the FAX. When the channel controller 4 receives an incomingcall from the external apparatus via the telephone line 3 (in step S20),the channel controller 4 informs the system controller 2 of it whilereceiving the image data (in step S21). The system controller 2instructs the control panel 10 to indicate that the FAX is receiving theimage data, and the system controller 2 drives the CODEC 7 (in stepS22). The CODEC 7 starts to decode each kind of image data (in stepS23), and arranges it in the image memory 6 (in step S24). When thecommunication is terminated (in step S25) and each kind of image data iscompletely arranged in the image memory 6, the system controller 2drives the plotter 8 (in step S26) so as to print out the image datastored in the image memory 6 (in step S27). When all the image data isprinted out (in step S28), the system controller 2 informs the controlpanel 10 of the termination and becomes a waiting mode so as toterminate the reception operation.

Further, the present invention is not limited to these preferredembodiments, and various variations and modifications may be madewithout departing from the scope of the present invention.

What is claimed is:
 1. An image data transmitter, comprising:a) imagesegmentation means for receiving image data including a plurality ofimage-data portions, and for segmenting the image data for eachimage-data portion so as to detect a kind of image data for eachimage-data portion, the image segmentation means including:1) firstmeans for performing a discrete cosine transformation on each block ofimage data, so as to provide discrete cosine transformed data for eachblock; 2) second means for determining the kind of image for each blockof image data based on the discrete cosine transformed data, so as toarrive at a determination result; and 3) third means for segmenting theimage data into portions representative of different kinds of images,based on the determination result; b) encoding means, coupled to saidimage segmentation means and compatible with plural kinds of codingschemes corresponding to a number of kinds of image data of theimage-data portions, for coding the image data for each image-dataportion in accordance with a corresponding one of the plural kinds ofcoding schemes, wherein said encoding means includes:1) means fordetermining a color of a character image from two color differencesignals of the image data if the image data represents a characterimage; and c) control means, coupled to said encoding means, forcontrolling transmission of the image data to an external apparatus. 2.The image data transmitter of claim 1, wherein the image segmentationmeans includes:1) means for performing a discrete cosine transformationfor each image-data portion so as to obtain a spectrum distribution of adiscrete cosine coefficient thereof; and 2) means for judging the kindof image data of each image-data portion by evaluating a level and aninversion frequency of said spectrum distribution.
 3. The image datatransmitter of claim 1, wherein:the image data transmitter comprises afacsimile apparatus capable of being coupled to an integrated servicesdigital network.
 4. An image data transmitter comprising:a) imagesegmentation means for receiving image data including a plurality ofimage-data portions, and for segmenting the image data for eachimage-data portion so as to detect a kind of image data for eachimage-data portion, the image segmentation means including:1) firstmeans for performing a discrete cosine transformation on each block ofimage data, so as to provide discrete cosine transformed data for eachblock; 2) second means for determining the kind of image for each blockof image data based on the discrete cosine transformed data, so as toarrive at a determination result; and 3) third means for segmenting theimage data into portions representative of different kinds of images,based on the determination result; b) encoding means, coupled to saidimage segmentation means and compatible with plural kinds of codingschemes corresponding to a number of kinds of image data of theimage-data portions, for coding the image data for each image-dataportion in accordance with a corresponding one of the plural kinds ofcoding schemes, wherein, if the image data represents a character image,wherein said encoding means includes:1) means for specifying a shape ofthe character image by binarizing the image data based on a luminancesignal thereof; and 2) means for coding the specified shape of thecharacter image; and c) control means, coupled to said encoding means,for controlling transmission of the image data to an external apparatus.5. The image data transmitter of claim 4, wherein the image segmentationmeans includes:1) means for performing a discrete cosine transformationfor each image-data portion so as to obtain a spectrum distribution of adiscrete cosine coefficient thereof; and 2) means for judging the kindof image data of each image-data portion by evaluating a level and aninversion frequency of said spectrum distribution.
 6. The image datatransmitter of claim 4, wherein:the image data transmitter comprises afacsimile apparatus capable of being coupled to an integrated servicesdigital network.
 7. An image data transmitter, comprising:a) imagesegmentation means for receiving image data including a plurality ofimage-data portions, and for segmenting the image data for eachimage-data portion so as to detect a kind of image data for eachimage-data portion, the image segmentation means including:1) firstmeans for performing a discrete cosine transformation on each block ofimage data, so as to provide discrete cosine transformed data for eachblock; 2) second means for determining the kind of image for each blockof image data based on the discrete cosine transformed data, so as toarrive at a determination result; and 3) third means for segmenting theimage data into portions representative of different kinds of images,based on the determination result; b) encoding means, coupled to saidimage segmentation means and compatible with plural kinds of codingschemes corresponding to a number of kinds of image data of theimage-data portions, for coding the image data for each image-dataportion in accordance with a corresponding one of the plural kinds ofcoding schemes, wherein said encoding means includes:1) means for usinga still picture coding scheme using a discrete cosine conversion, so asto obtain a discrete cosine conversion coefficient of the image data foreach image-data portion; 2) a quantizing memory for storing a pluralityof thresholds corresponding to a number of kinds of image data of theimage-data portions; and 3) means for dividing the discrete cosineconversion coefficient by a corresponding one of the thresholds; and c)control means, coupled to said encoding means, for controllingtransmission of the image data to an external apparatus.
 8. The imagedata transmitter of claim 7, wherein the image segmentation meansincludes:1) means for performing a discrete cosine transformation foreach image-data portion so as to obtain a spectrum distribution of adiscrete cosine coefficient thereof; and 2) means for judging the kindof image data of each image-data portion by evaluating a level and aninversion frequency of said spectrum distribution.
 9. The image datatransmitter of claim 7, wherein:the image data transmitter comprises afacsimile apparatus capable of being coupled to an integrated servicesdigital network.
 10. A method for transmitting image-data including aplurality of image-data portions to an external apparatus, said methodcomprising the steps of:a) segmenting the image data for each image-dataportion so as to detect a kind of image data for each image-dataportion, the segmenting step including the steps of:1) performing adiscrete cosine transformation on each block of image data, so as toprovide discrete cosine transformed data for each block; 2) determiningthe kind of image for each block of image data based on the discretecosine transformed data, so as to arrive at a determination result; and3) segmenting the image data into portions representative of differentkinds of images, based on the determination result; b) coding the imagedata for each image-data portion in accordance with a coding schemecorresponding to the kind of image data of the image data portion,wherein said step of coding the image data includes:1) coding datarepresenting a shape of a character image and transmitting coded imagedata to the external apparatus with data representing a color of thecharacter image, if the image data represents a character image; and c)transmitting the image data to the external apparatus.
 11. A methodaccording to claim 10, wherein, if the image data represents a characterimage including a plurality of colors, the step of transmitting theimage data includes:transmitting the image data for each color of thecharacter image.